Short-circuit member for a commutator and an armature

ABSTRACT

The number of conductor members in a first conductor member group and the number of conductor members in a second conductor member group are equal to each other. An inner terminal of each conductor member is displaced from an outer terminal of the same conductor member with respect to the circumferential direction of the corresponding conductor member group. Each outer terminal of the first conductor member group is displaced from a corresponding one of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group.

BACKGROUND OF THE INVENTION

The present invention relates to a short-circuit member that short-circuits predetermined segments to each other so that they have the same potential, a commutator having the short-circuit member, an armature having the commutator, and a method for manufacturing the short-circuit member.

In a motor such as a direct-current motor having a commutator and feeding brushes sliding against the commutator, a current is supplied to armature coils of an armature through the feeding brushes and the commutator. The commutator has a number of segments, and predetermined ones of the segments are short-circuited by a short-circuit member. By short-circuiting the predetermined segments, a current is supplied to segments that are not contacting the feeding brushes. The number of feeding brushes can be reduced.

For example, Japanese Laid-Open Patent Publication No. 2005-137193 discloses a short-circuit member that is formed by stacking a first conductor member group and a second conductor member group. Each of the first and second conductor member group includes conductor members the number of which is equal to the number of the segments of the commutator. The conductor members in each conductor member group are arranged to form a circle. Each conductor member has an outer terminal located at an outer portion with respect to the radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling portion coupling the outer terminal and the inner terminal to each other. A hook portion extending radially outward of the corresponding conductor member group is formed in the outer terminal of each conductor member. The first conductor member group and the second conductor member group are stacked on each other such that the outer terminals of the first conductor member group and the outer terminals of the second conductor member group are aligned and the inner terminals of the first conductor member group and the inner terminals of the second conductor member group are aligned. The aligned outer terminals are joined, and the aligned inner terminals are joined, so that the first and second conductor member groups are integrated. The hook portions of the outer terminals of the integrated first and second conductor member groups are connected to the corresponding segments. Some of the hock portions are engaged with end portions of the corresponding armature coils.

In the short-circuit member of the above described publication, each outer terminal of the first conductor member group is joined with the corresponding one of the outer terminals of the second conductor member group, and each inner terminal of the first conductor ember group is joined with the corresponding one of the inner terminals of the second conductor member group. In other words, joining is required at a number of positions. This complicates the operation for integrating the first conductor member group and the second conductor member group.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a short-circuit member that simplifies an operation for integrating a first conductor member group and a second conductor member group, a commutator having the short-circuit member, an armature having the commutator, and a method for manufacturing the short-circuit member.

To achieve the foregoing objective and in accordance with a first aspect of the present invention, a short-circuit member including a first conductor member group and a second conductor member group is provided. Each conductor member group includes a plurality of conductor members that are arranged to form a circle. The number of the conductor members belonging to the first conductor member group and the number of the conductor members belonging to the second conductor member group being equal to each other and represented by n. Each conductor member has an outer terminal located at an outer portion with respect to a radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling portion coupling the outer terminal and the inner terminal to each other. The inner terminal of each conductor member is displaced from the outer terminal of the same conductor member with respect to a circumferential direction of the corresponding conductor member group. The first conductor member group and the second conductor member group are stacked on each other such that the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the first conductor member group is opposite to the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the second conductor member. Each inner terminal of the first conductor member group is aligned with a corresponding one of the inner terminals of the second conductor member group. Each outer terminal of the first conductor member group is displaced from a corresponding one of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group.

In accordance with a second aspect of the present invention, a commutator including segments and short-circuit member is provided. The number of the segments is represented by 2n, n being a positive integer. The short-circuit member has a first conductor member group and a second conductor member group. Each conductor member group includes a plurality of conductor members that are arranged to form a circle. The number of the conductor members belonging to the first conductor member group and the number of the conductor members belonging to the second conductor member group are equal to each other and represented by n. Each conductor member has an outer terminal located at an outer portion with respect to a radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling, portion coupling the outer terminal and the inner terminal to each other. The inner terminal of each conductor member is displaced from the outer terminal of the same conductor member with respect to a circumferential direction of the corresponding conductor member group. The outer terminal of each conductor member is connected to the corresponding one of the segments. The first conductor member group and the second conductor member group are stacked on each other such that the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the first conductor member group is opposite to the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the second conductor member. Each inner terminal of the first conductor member group is aligned with a corresponding one of the inner terminals of the second conductor member group. Each outer terminal of the first conductor member group is displaced from a corresponding one of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group.

In accordance with a third aspect of the present invention, an armature including a rotary shaft and an armature core fixed about the rotary shaft is provided. A coil is wound about the armature core. The armature core is further provided with the commutator according to the second aspect of the present invention that is fixed about the rotary shaft. The segments of the commutator are electrically connected to the coil.

In accordance with a fourth aspect of the present invention, a method for manufacturing the short-circuit member according to the first aspect of the present invention is provided. The method includes: forming on each of two conductive plates a conductor member group formed of annularly arranged conductor members, the conductor members in the conductor member group formed on each conductive plate being connected one another by an outer frame and an inner frame. The forming the conductor member group includes: punching through pressing annularly arranged outer holes and annularly arranged inner holes, the numbers of which are equal to each other, on each plate, whereby an outer terminal is formed between each circumferentially adjacent pair of the outer holes, and an inner terminal is formed between each circumferentially adjacent pair of the inner holes, and forming through pressing cutting lines the number of which, is the equal to the numbers of the outer holes and the inner holes, the cutting lines being located in a part of each plate located between the outer holes and the inner holes, each cutting line extending from one of the outer holes toward the corresponding one of the inner holes, thereby dividing the part of the plate between the outer holes and the inner holes so that coupling portions are formed. The method further includes bending the coupling portion of each conductor member belonging to the conductor member group formed on each plate such that a center portion of each coupling portion bulges in a direction of the thickness of the plate, the bending of the coupling portions causes a circumferentially adjacent coupling portions to be separate from each other; stacking the plates onto each other after bending, such that the direction in which the center portion of each coupling portion of one of the plates bulges and the direction in which the center portion of each coupling portion of the other plate bulges are opposite to each other, wherein, in the stacked plates, the inner terminals of one of the plates are aligned with the inner terminals of the other plate, and the outer terminals of one of the plates are displaced from the outer terminals of the other plate; and removing the outer frame and the inner frame of each plate after the stacking of the plates.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an armature according to a first embodiment of the present invention taken along a center axis of the armature, showing one of the halves divided at the center axis;

FIG. 2 is a half cross-sectional view showing a commutator of the armature shown in FIG. 1;

FIG. 3 is a plan view showing a conductor bar assembly of the armature shown in FIG. 1;

FIG. 4 is a plan view showing a conductor bar group of the armature shown in FIG. 1;

FIGS. 5A, 5B, and 5C are diagrams showing manufacturing procedure of the conductor bar assembly shown in FIG. 3;

FIG. 6 is a plan view showing a conductor bar assembly according to a second embodiment of the present invention;

FIG. 7 is an exploded perspective view showing the bar assembly shown in FIG. 6;

FIGS. 8, 9, 10, and 11 are diagrams showing manufacturing procedure of the conductor bar assembly shown in FIG. 6;

FIG. 12 is a plan view showing a conductor bar assembly according to a modified embodiment of the present invention; and

FIG. 13 is a plan view showing a conductor bar assembly according to another modified embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will now be described with reference to the drawings.

An armature 1 shown in FIG. 1 is arranged inside of a stator (not shown), and form a motor together with the stator. The stator has permanent magnets that are arranged along the circumferential direction of the armature 1.

The armature 1 includes a metal rotary shaft 2, an armature core 3, a commutator 4, and coils 5 wound about the armature core 3. The armature core 3 and the commutator 4 are fixed to the periphery of the rotary shaft 2. Both ends of the rotary shaft 2 are rotatably supported by the stator.

The armature core 3 includes an annular fixing portion 3 a and teeth 3 b extending radially outward from the outer periphery of the fixing portion 3 a. The fixing portion 3 a has a hole through which the rotary shaft 2 extends. The coils 5 are wound about the teeth 3 b.

The commutator 4 includes a commutator main body 11 fixed to the rotary shaft 2 and a short-circuit member 12 arranged at one end of the commutator main body 11. The commutator main body 11 includes an insulation member 13 contacting the rotary shaft 2 and sixteen segments 14 located on the outer periphery of the insulation member 13. The insulation member 13 is made of, for example, an insulating thermosetting resin and is substantially cylindrical. One end of the insulation member 13 (the lower end as viewed in FIG. 1) forms a joining portion 13 a of a small diameter. The rotary shaft 2 is press fitted to the inside of the joining portion 13 a so that the insulation member 13 is fixed to the rotary shaft 2. The insulation member 13 thus rotates integrally with the rotary shaft 2.

As shown in FIG. 2, the segments 14 are arranged on the outer circumferential surface of the insulation member 13 at equal angular intervals. Each segments 14 substantially has an elongated shape along the axial direction of the commutator 4. A pair of holding claws 14 a extend from the inner surface of each segment 14. The holding claws 14 a are curved such that each pair approach each other toward the distal ends. Each segment 14 is held by the insulation member 13 by embedding the holding claws 14 a into the insulation member 13. Each segment 14 has a riser 14 b, with which an end of the corresponding coil 5 is engaged. Each riser 14 b extends from the outer surface of one end of the corresponding segment 14 (the outer surface of the lower end in FIG. 2), and forms an acute angle with the outer surface of the segment 14. A plurality of non-illustrated feeding brushes slide against the commutator main body 11, which is formed by the insulation member 13 and the segments 14 as described above, from radially outward positions.

The short-circuit member 12 includes a conductor bar assembly (conductor member assembly) 21 and a holding member 22. The conductor bar assembly 21 short-circuits each pair of the segments 14 that are spaced by 180 degrees along the circumferential direction of the commutator 4. The holding member 22 holds the conductor bar assembly 21.

As shown in FIG. 3, the conductor bar assembly 21 is formed by stacking a first conductor bar group (first conductor member group) 23 and a second conductor bar group (second conductor member group) 23. Each of the conductor bar groups 23 includes four first conductor bars (first conductor members) 24 and four second conductor bars (second conductor members) 25. When viewed along the center axis of the conductor bar groups 23, the first conductor bar group 23 and the second conductor bar group 23 have identical but inverted shapes.

As shown in FIG. 4, the eight conductor bars 24, 25 of each conductor bar group 23 are arranged to form a circle. Each conductor bar 24, 25 has an outer terminal 26 and an inner terminal 27. The outer terminals 26 are located outside of the inner terminals 27 with respect to the radial direction of the corresponding conductor bar group 23. The inner terminals 27 are located inside of the outer terminals 26 with respect to the radial direction of the corresponding conductor bar group 23. In each of the conductor bar groups 23, the four first conductor bars 24 are consecutively arranged along the circumferential direction of the conductor bar group 23 to form a half of the conductor bar group 23 (lower half as viewed in FIG. 4). The four second conductor bars 25 are consecutively arranged along the circumferential direction of the conductor bar group 23 to form the other half of the conductor bar group 23 (upper half as viewed in FIG. 4). The inner terminal 27 of each first conductor bar 24 is displaced from the outer terminal 26 of the same first conductor bar 24 along the circumferential direction of the conductor bar group 23 by a predetermined first angle θ1, specifically, by 101.25 degrees. The outer terminal 26 and the inner terminal 27 of each first conductor bar 24 are coupled to each other by a first coupling portion 28 a. The inner terminal 27 of each second conductor bar 25 is displaced from the outer terminal 26 of the same second conductor bar 25 along the circumferential direction of the conductor bar group 23 by a predetermined second angle θ2, specifically, by 78.75 degrees. The outer terminal 26 and the inner terminal 27 of each second conductor bar 25 are coupled to each other by a second coupling portion 28 b, which is shorter than the first coupling portion 28 a. Each coupling portion 28 a, 28 b is curved to form an involute curve when viewed along the center axis of the corresponding conductor bar group 23.

A space having a substantially constant width exists between the coupling portions 28 a, 28 b of each pair of the conductor bars 24, 25 that arc adjacent to each other with respect to the circumferential direction of the conductor bar group 23.

A small imaginary circle C1 in FIG. 4 is formed by connecting positions at which the inner terminals 27 of each conductor bar group 23 are arranged. A large imaginary circle C2 in FIG. 4 is formed by connecting positions at which the outer terminals 26 of each conductor bar group 23 are arranged. A first imaginary straight line L1 extends in the longitudinal direction in FIG. 4 and includes a center O1 common to the small circle C1 and the large circle C2. A second imaginary straight line L2 extends in the lateral direction in FIG. 4 and includes the center O1. The straight lines L1 and L2 are perpendicular to each other.

When the number of the segments 14 of the commutator 4, which is sixteen, is expressed as 2n, n represents eight, which is an even number. The value of n is equal to the number of the outer terminals 26 of each conductor bar group 23 and to the number of the inner terminals 27 of each conductor bar group 23.

The inner terminals 27, the number of which is represented by n (n−8, in this embodiment), of each conductor bar group 23 are arranged on the small circle C1 at equal angular intervals, such that each inner terminal 27 is axisymmetric with the corresponding one of the inner terminals 27 with respect to the first straight line L1. At this time, no inner terminal 27 is located on the first straight line L1 and the second straight line L2.

The outer terminals 26, the number of which is represented by n (n=8, in this embodiment), of each conductor bar group 23 are arranged on the large circle C2 at equal angular intervals, such that each outer terminals 26 is axisymmetric with the corresponding one of the outer terminals 26 with respect to the second straight line L2. At this time, first one of the outer, terminals 26 that are arranged on a half of the large circle C2, which is divided into two by the second straight line L2 is displaced from the second straight line L2 by the angle corresponding to the half of the angular interval (360/2n)° between each adjacent pair of the segments 14 along the circumferential direction of the commutator 4, that is, by (360/4n)°. The remaining outer terminals 26, the number of which is represented by (n/2)−1, are each arranged to be displaced from the first outer terminal 26 by 1×(360/n)°, 2×(360/n)°, (n/2−1)×(360/n)°.

Among the outer terminals 26 of each conductor bar group 23, the number of the ones that are arranged on a half of the large circle C2, which is divided into two by the second straight line L2, is represented by n/2 (in FIG. 4, the four outer terminals 26 located in the lower half of the large circle C2). Each of these outer terminals 26 is coupled, by means of the first coupling portion 28 a, to an inner terminal 27 that is displaced from the same outer terminal 26 with respect to the circumferential direction of the conductor bar group 23 by the first angle θ1. Each of the remaining of the outer terminals 26, the number of which is represented by n/2 (the four outer terminals 26 located in the upper half of the large circle C2 in FIG. 4) is coupled, by means of the second coupling portion 28 b, to ah inner terminal 27 that is displaced from the same outer terminal with respect to the circumferential direction of the conductor bar group 23 by the second angle θ2. The first angle θ1 corresponds to (90+(360/(4n)))°, and the second angle θ2 corresponds to (90−(360/(4n)))°.

Referring back to FIG. 3, the first conductor bar group 23 and the second conductor bar group 23 are stacked on each other after one of the first and second conductor bar groups 23 is inverted about the first straight line L1. The stacking is executed such that each of the inner terminals 27 of the first conductor bar group 23 is aligned with the corresponding one of the inner terminals 27 of the second conductor bar group 23, and that each of the outer terminals 26 of the first conductor bar group 23 is displaced from the corresponding one of the outer terminals 26 of the second conductor bar group 23 with respect to the circumferential direction of the corresponding conductor bar group 23. In the conductor bar assembly 21, which is obtained by stacking the first and second conductor bar groups 23, sixteen outer terminals 26 are arranged at equal angular intervals along the circumferential direction of the conductor bar assembly 21. Also, the direction in which the inner terminal 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the first conductor bar group 23 is opposite to the direction in which the inner terminal 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the second conductor bar group 23. Further, regarding each pair of a conductor bar 24, 25 of the first conductor bar group 23 and a conductor bar 24, 25 of the second conductor bar group 23, of which the inner terminals 27 are aligned with each other, the linear distance between the inner terminal 27 and the outer terminal 26 of one of the conductor bars 24, 25 is different from that of the other.

As shown in FIG. 2, each coupling portion 28 a, 28 b of the first conductor bar group 23 or each coupling portion 28 a, 28 b of the second conductor bar group 23 is bent such that its center portion in the longitudinal direction bulges by a relatively great amount in the axial direction of the conductor bar assembly 21, and each coupling portion 28 a, 28 b of the other conductor bar group 23 is bent such that its center portion in the longitudinal direction bulges by a relatively small amount in the axial direction of the conductor bar assembly 21. Therefore, the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23 have three-dimensional shapes. The direction in which the center portions of the coupling portions 28 a, 28 b with greatly bulging center portion bulge is a direction away from the conductor bar group 23 that is different from the conductor bar group 23 to which the coupling portions 28 a, 28 b of the greatly bulging center portions belong. The direction in which the center portions of the coupling portions 28 a, 28 b with slightly bulging center portion bulge is a direction toward the conductor bar group 23 that is different from the conductor bar group 23 to which the coupling portions 28 a, 28 b of the slightly bulging center portions belong.

Each aligned pair of the inner terminals 27 of the first conductor bar group 23 and the inner terminals 27 of the second conductor bar group 23 are joined to each other through welding. On the other hand, the outer terminals 26 of the first conductor bar group 23 and the outer terminals 26 of the second conductor bar group 23 are not joined to each other. Thus, the conductor bar assembly 21 only has eight joined positions. As shown in FIG. 3, in the conductor bar assembly 21, the outer terminals 26 of each pair of a first conductor bar 24 and a second conductor bar 25 the inner terminals 27 of which are joined to each other are spaced by 180 degrees along the circumferential direction of the conductor bar assembly 21.

As shown in FIG. 2, the holding member 22, which holds the conductor bar assembly 21, is formed of a material different from that of the insulation member 13. The holding member 22 is made of, for example, an insulating thermoplastic resin and is substantially annular. A portion of the conductor bar assembly 21 except for the outer terminals 26 is embedded in the holding member 22 so that the conductor bar assembly 21 is held by the holding member 22. The resin forming the holding member 22 fills not only the space between the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23, but also the space between each circumferentially adjacent pair of the conductor bars 24, 25 (see FIG. 3). A cylindrical boss 22 a extends from a center of the holding member 22. The inner diameter of the boss 22 a is equal to or slightly smaller than the outer diameter of the joining portion 13 a of the insulation member 13. The joining portion 13 a is press fitted to the boss 22 a, so that the short-circuit member 12 is attached and fixed to the commutator main body 11. In the state where the short-circuit member 12 is attached to the commutator main body 11, each outer terminal 26 contacts one end of the corresponding segment 14 (the lower end as viewed in FIG. 2). Contacting parts of the outer terminals 26 and the segments 14 are welded to each other so as to be; electrically conducted to each other. Accordingly, each pair of the segments 14 that are spaced by 180 degrees along the circumferential direction of the commutator 4 are short-circuited and maintained at a same potential.

As shown in FIG. 1, the armature core 3 and the commutator 4 are arranged along the axial direction of the rotary shaft 2 and fixed about the rotary shaft 2. The distal end of the boss 22 a of the commutator 4 contacts the armature core 3. The boss 22 a supports an end of each coil 5 that is routed from the riser 14 b of each segment 14 to a tooth 3 b of the armature core 3. This supported end of each coil 5 will hereafter be referred to as a connecting wire 5 a. That is, the boss 22 a prevents the connecting wires 5 a from contacting the rotary shaft 2, and also prevents the connecting wires 5 a from being bent by a small bending radius.

A method for manufacturing the short-circuit member 12 will now be described.

First, as shown in FIG. 5A, each of two conductive plates 31 such as copper plates is pressed to punch annularly arranged eight slits 32. This forms eight conductor bars 24, 25 each located between an adjacent pair of the slits 32 of each plate 31. The conductor bars 24, 25 formed in each plate 31 are connected by an outer frame 33 and an inner frame 34. In the present embodiment, the coupling portion 28 a, 28 b of each conductor bar 24, 25 is bent such that its longitudinal center portion bulges along the direction of the thickness of the corresponding plate 31 at the same time as punching.

Next, the pressed two plates 31 are stacked as shown in FIG. 5C. Prior to the stacking, one of the two plates 31 is inverted about the first straight line L1 shown in FIG. 5A. FIG. 5B shows the inverted plate 31. Accordingly, when the two plates 31 are stacked, the direction in which the inner terminal 27 is displaced from the outer terminal 26 of each conductor bar 24, 25 in one plate 31 is opposite to the direction in which the inner terminal 27 is displaced from the outer terminal 26 of each conductor bar 24, 25 in the other plate 31. Also, the inner terminals 27 of one plate 31 are arranged to be aligned with the inner terminals 27 of the other plate 31, and the outer terminals 26 of one plate 31 are arranged to be displaced from the outer terminals 26 of the other plate 31.

Subsequently, the aligned pairs of the inner terminals 27 of the stacked two plates 31 are joined through welding.

Thereafter, to form the holding member 22, the stacked two plates 31 are placed in a mold (not shown), which is then filled with molten thermoplastic resin. The thermoplastic resin is cooled and solidified, so that the holding member 22, which is integrated with the stacked two plates 31, is completed. After the completion of the holding member 22, the two plates 31, which is integrated with the holding member 22, is removed from the mold.

Finally, the plates 31 are cut along double dashed lines in FIG. 5C to remove the outer frame 33 and the inner frame 34 of each plate 31. The short-circuit member 12 is thus completed.

The first embodiment provides the following advantages.

(1) Each pair of the segments 14 that are spaced by 180 degrees along the circumferential direction of the commutator 4 are short-circuited to each other by two of the conductor bars 24, 25, which are one of the conductor bars 24, 25 in the first conductor bar group 23 and one of the conductor bars 24, 25 in the second conductor bar group 23. Therefore, the number of the conductor bars 24, 25 in each conductor bar group 23 is eight, which is less than that in the prior art. While the inner terminals 27 of the first conductor bar group 23 and the inner terminals 27 of the second conductor bar group 23 are aligned and joined to each other, the outer terminals 26 of the first conductor bar group 23 and the outer terminals 26 of the second conductor bar group 23 are displaced and not joined to each other. When integrating the first conductor bar group 23 and the second conductor bar group 23, the number of parts that require joining is eight, which is less that in the prior art. Therefore, the first conductor bar group 23 and the second conductor bar group 23 are easily integrated, which improves the productivity of the commutator 4 and the armature 1. The small number of the joining parts reduces the incidence of poor joining, and thus increases the reliability of the short-circuit member 12. As a result, the segments 14 that are short-circuited by the short-circuit member 12 are reliably conducted to each other, so that current is reliably supplied to the coils 5 through the commutator 4. Further, since the number of the conductor bars 24, 25 that belong to each conductor bar group 23 is less than that of the prior art, there is no harm in widening the width of the coupling portion 28 a, 28 b of each conductor bar 24, 25. For example, when increasing the width of each coupling portion 28 a; 28 b without changing the value of its electric resistance (that is, without changing the cross-sectional area along the width of the coupling portion 28 a, 28 b), the thickness of the coupling portion 28 a, 28 b does not need to be significantly increased. Thus, plates 31 having relatively small thicknesses can be used for forming the conductor bar groups 23. The thinner the plates 31, the easier and more accurate the punching becomes. Alternatively, when the width of each coupling portion 28 a, 28 b is increased without changing its thickness, the cross-sectional area along the width of the coupling portion 28 a, 28 b is increased. This reduces the electric resistance of the coupling portion 28 a, 28 b, and thus improves the conductivity of the connection between the segments 14 that are short-circuited by the short-circuit member 12.

(2) The eight inner terminals 27 of each conductor bar group 23 are arranged at equal angular intervals along the circumferential direction of the conductor bar group 23. That is, the distance between each adjacent pair of the inner terminals 27 with respect to the circumferential direction of the corresponding conductor bar group 23 is constant. This facilitates the joining of the corresponding inner terminals 27 to each other, prevents adjacent inner terminals 27 along the circumferential direction of the conductor bar group 23 from contacting each other and being short-circuited.

(3) In addition to the fact that the inner terminals 27 of each conductor bar group 23 are arranged at equal angular intervals along the circumferential direction of the conductor bar group 23, each inner terminal 27 is displaced by the first angle θ1 or the second angle θ2 with respect to the circumferential direction of the conductor bar group 23 from the outer terminal 26 of the associated conductor bar 24, 25. Therefore, when the first conductor bar group 23 and the second conductor bar group 23 are stacked such that the inner terminals 27 are aligned, the sixteen outer terminals 26 are arranged at equal angular intervals along the circumferential direction of the conductor bar groups 23. This facilitates the operation for connecting the outer terminals 26 to the segments 14, which are arranged at equal angular intervals along the circumferential direction of the commutator 4.

(4) When viewed along the center axis of the corresponding conductor bar group 23, the first conductor bar group 23 and the second conductor bar group 23 have identical shapes. The eight inner terminals 27 of each conductor bar group 23 are arranged on the small circle C1 shown in FIG. 4 at equal angular intervals, such that each inner terminal 27 is axisymmetric with the corresponding one of the inner terminals 27 with respect to the first straight line L1. The eight outer terminals 26 of each conductor bar group 23 are arranged on the large circle C2 shown in FIG. 4 at equal angular intervals, such that each outer terminal 26 is axisymmetric with the corresponding one of the outer terminals 26 with respect to the second straight line L2. Therefore, when the first conductor bar group 23 and the second conductor bar group 23 are stacked after inverting one of the first conductor bar group 23 and the second conductor bar group 23 about the first straight line L1, each inner terminal 27 of the first conductor bar group 23 is aligned with the corresponding inner terminal 27 of the second conductor bar group 23, and each outer terminal 26 of the first conductor bar group 23 is displaced in the circumferential direction of the conductor bar group 23 from the corresponding outer terminal 26 of the second conductor bar group 23. This facilitates the stacking of the first conductor bar group 23 and the second conductor bar group 23, and thus improves the productivity of the short-circuit member 12.

(5) The number of the conductor bars 24, 25 belonging to each conductor bar group 23 is less than that in the prior art. Thus, by increasing the width of the slits 32, which are punched in the plates 31 through pressing, the distance between each adjacent pair of the conductor bars 24, 25 with respect to the circumferential direction of the corresponding conductor bar group 23 is easily made wider than that in the prior art. The wider the slits 32, the easier the punching of the slits 32 becomes. Also, the conductor bars 24, 25 each formed between adjacent slits 32 are prevented from being deformed when the slits 32 are formed. Further, compared to the case where the slits 32 have narrow widths, a mold such as a punch and a die used in pressing is easily produced, and the life of the mold is extended.

(6) Each coupling portion 28 a, 28 b of the first conductor bar group 23 or each coupling portion 28 a, 28 b of the second conductor bar group 23 is bent such that its center portion in the longitudinal direction bulges by a relatively great amount in the axial direction of the corresponding conductor bar group 23. The direction in which the center portions bulge is a direction away from the other conductor bar group 23. Therefore, a sufficiently large space is easily created between each adjacent pair of the coupling portions 28 a, 28 b along the circumferential direction of the corresponding conductor bar group 23 to prevent the coupling portions 28 from being short-circuited, without reducing the width of each coupling portion 28 a, 28 b, changing the space between adjacent outer terminals 26 along the circumferential direction of the corresponding conductor bar group 23 or the space between the adjacent inner terminals 27 along the circumferential direction of the corresponding conductor bar group 23, or changing the outer diameter or the inner diameter of each conductor bar group 23. This also prevents the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23 from contacting each other and being short-circuited.

Second Embodiment

A second embodiment of the present invention will now be described with reference to the drawings. The differences from the first embodiment will mainly be discussed below.

Instead of the conductor bar assembly 21 of the first embodiment shown in FIG. 3, the short-circuit member 12 according to the second embodiment is provided with a conductor bar assembly 61 shown in FIG. 6. The conductor bar assembly 61 is formed by stacking a first conductor bar group 62 and a second conductor bar group 62, each having four first conductor bars 63 and four second conductor bars 64. When viewed along the center axis of the corresponding conductor bar group 62, the first and second conductor bar groups 62 have identical but inverted shapes. Comparing the first and second conductor bar groups 62 shown in FIG. 6 and the first and second conductor bar groups 23 shown in FIG. 3, the shape of a coupling portion 65 that couples the outer terminal 26 to the inner terminal 27 of each of the first and second conductor bars 63, 64 belonging to the conductor bar groups 62 is different from that of the coupling portion 28 a, 28 b of each of the conductor bars 23 belonging to the conductor bar groups 23.

The eight conductor bars 63, 64 of each conductor bar group 62 are arranged to form a circle. As in the first embodiment, the inner terminal 27 of each first conductor bar 63 is displaced from the outer terminal 26 of the same first conductor bar 63 along the circumferential direction of the conductor bar group 62 by a predetermined first angle θ1, specifically, by 101.25 degrees. The inner terminal 27 of each second conductor bar 64 is displaced from the outer terminal 26 of the same second conductor bar 64 along the circumferential direction of the conductor bar group 23 by a predetermined second angle θ2, specifically, by 78.75 degrees. Each coupling portion 65 a, 65 b is curved to form an involute curve when viewed along the center axis of the corresponding conductor bar group 62.

As shown in FIG. 7, the outer terminals 26 and the inner terminals 27 of each conductor bar group 62 are arranged in a common plane, while the coupling portions 65 a, 65 b of each conductor bar group 62 are bent such that their center portions bulge in the axial direction of the bar assembly 61. The direction in which the center portions of the coupling portions 65, 65 b bulge is a direction away from the conductor bar group 62 that is different from the conductor bar group 62 to which the coupling portions 65 a, 65 b belong. The bend of each coupling portion 65 a, 65 b is formed by substantially orthogonally bending the corresponding conductor bar 63, 64 at two positions near the boundary between the outer terminal 26 and the coupling portion 65 a, 65 b, and substantially orthogonally bending the conductor bar 63, 64 at two positions near the boundary between the inner terminal 27 and the coupling portion 65 a, 65 b. Therefore, each coupling portion 65 a, 65 b has a channel-like longitudinal cross-sectional shape.

Each adjacent pair of the coupling portions 65 a, 65 b along the circumferential direction of the corresponding conductor bar group 62 contact each other at part of their side faces 65 c, 65 d before the coupling portions 65 a, 65 b are bent, that is, when the coupling portions 65 a, 65 b are located in the same plane as the outer terminals 26 and the inner terminals 27. Each adjacent pair of the coupling portions 65 a, 65 b are separated from each other only by bending the coupling portions 65 a, 65 b. The coupling portions 65 a, 65 b are wider than the coupling portions 28 a, 28 b according to the first embodiment shown in FIG. 3.

As shown in FIG. 6, the first conductor bar group 62 and the second conductor bar group 62 are stacked on each other after one of the first and second conductor bar groups 23 is inverted about the first straight line L1, such that the direction in which the center portion of each coupling portion 65 a, 65 b of the first conductor bar group 62 bulges and the direction in which the center portion of each coupling portion 65 a, 65 b of the second conductor bar group 62 bulges are opposite to each other. The stacking is executed such that each of the inner terminals 27 of the first conductor bar group 62 is aligned with the corresponding one of the inner terminals 27 of the second conductor bar group 62, and that each of the outer terminals 26 of the first conductor bar group 62 is displaced from the corresponding one of the outer terminals 26 of second conductor bar group 62 with respect to the circumferential direction of the corresponding conductor bar group 62. In the conductor bar assembly 61, which is obtained by stacking the first and second conductor bar groups 62, sixteen outer terminals 26 are arranged at equal angular intervals along the circumferential direction of the conductor bar assembly 61. Also, the direction in which the inner terminal 27 is displaced from the outer terminal 26 in each conductor bar 63, 64 in the first conductor bar group 62 is opposite to the direction in which the inner terminals 27 is displaced from the outer terminal 26 in each conductor bar 63, 64 in the second conductor bar group 62. Further, regarding each pair of a conductor bar 63, 64 of the first conductor bar group 62 and a conductor bar 63, 64 of the second conductor bar group 62, of which the inner terminals 27 are aligned with each other, the linear distance between the inner terminal 27 and the outer terminal 26 of one of the conductor bars 63, 64 is different from that of the other.

A method for manufacturing the short-circuit member 12 having the conductor bar assembly 61 of the above described configuration will now be described.

First, as shown in FIG. 8, each of two conductive plates 71 such as copper plates is pressed to form the conductor bar group 62 including annularly arranged eight conductor bars 63, 64.

More specifically, annularly arranged eight outer holes 72 and annularly arranged eight inner holes 73 are formed in each plate 71 through punching. An outer terminal 26 is formed between each adjacent pair of the outer holes 72 in the circumferential direction of the outer holes 72, and an inner terminal 27 is formed between each adjacent pair of the inner holes 73 in the circumferential direction of the inner holes 73.

Next, eight cutting lines 74 are formed at positions in each plate 71 between the outer holes 72 and the inner holes 73 through pressing. In FIG. 8, the cutting lines 74 are shown by double dashed lines. Each cutting line 74 extends from one of the outer holes 72 to the corresponding inner hole 73. The cutting lines 74 divides a portion of each plate 71 located between the outer holes 72 and the inner holes 73 into annularly arranged eight pieces, thereby forming the eight coupling portions 65 a, 65 b. The conductor bars 63, 64 of the conductor bar group 62 formed in each plate 71 are connected by an outer frame 33 and an inner frame 34. Each adjacent pair of the coupling portions 65 a, 65 b in the circumferential direction of the corresponding conductor bar group 62 contact each other at their side faces 65 c, 65 d.

Next, each coupling portion 65 a, 65 b is bent such that its center portion bulges along the thickness of the plate 71. As shown in FIG. 9, the coupling portions 65 a, 65 b are bent by a first mold 81 having an annular projection 81 a and a second mold 82 having an annular recess 82 a, which corresponds to the projection 81 a. The projection 81 a and the recess 82 a are each formed to correspond to the coupling portions 65 a, 65 b of the plates 71. After the plate 71 shown in FIG. 8 is placed between the first mold 81 and the second mold 82, the first mold 81 and the second mold 82 are brought closer, so that the plate 71 is held between the molds 81, 82. This bends the coupling portions 65 a, 65 b on the plate 71 as shown in FIG. 10, and each adjacent pair of the coupling portions 65 a, 65 b in the circumferential direction of the conductor bar group 62 are separated from each other.

Then, the two plates 71 shown in FIG. 10 are stacked on each other. Prior to the stacking, one of the two plates 71 is inverted about the first straight line L1 shown in FIG. 10. At the stacking, the two plates 71 are arranged such that the direction in which the center portion of each coupling portion 65 a, 65 b of the first conductor bar group 62 bulges and the direction in which the center portion of each coupling portion 65 a, 65 b in the second conductor bar group 62 bulges are opposite to each other.

Thereafter, the aligned pairs of the inner terminals 27 of the stacked two plates 71 are joined through welding. The integrated two plates 71 are used as an insert, and the holding member 22 is insert molded as in the case of the first embodiment. Finally, the plates 71 are cut along double dashed lines in FIG. 11 to remove the outer frame 33 and the inner frame 34 of each plate 71. The short-circuit member 12 having the conductor bar assembly 61 is thus completed.

In addition to the advantages (1) to (5) of the first embodiment, the second embodiment provides the following advantages.

(1) Each pair of adjacent coupling portions 65 a, 65 b in the circumferential direction of the corresponding conductor bar group 62 contact each other before the coupling portions 65 a, 65 b are bent, and are separated from each other only when the coupling portions 65 a, 65 b are bent. A sufficient space is needed between each adjacent pair of the coupling portions 65 a, 65 b along the circumferential direction of the conductor bar group 62 to prevent the coupling portions 65 a, 65 b from contacting each other before the coupling portions 65 a, 65 b are bent. However, since there is no harm in allowing adjacent coupling portions 65 a, 65 b to contact before the coupling portions 65 a, 65 b are bent, such space is not required in the present embodiment. Therefore, the width of the coupling portion 65 a, 65 b of each conductor bar 63, 64 is easily widened without changing the inner diameter or the outer diameter of each conductor bar group 62, or changing the space between adjacent outer terminals 26 in the circumferential direction of the conductor bar group 62 or the space between adjacent inner terminals 27 in the circumferential direction of the conductor bar group 62. When the width of each coupling portion 65 a, 65 b is increased, the cross-sectional area along the width of the coupling portion 65 a, 65 b is increased. This reduces the electric resistance of the coupling portion 65 a, 65 b, and thus improves the conductivity of the connection between the segments 14 that are short-circuited by the short-circuit member 12.

(2) During the manufacture of the short-circuit member 12 according to the second embodiment, the conductor bars 63, 64 are formed in each plate 71 by forming the cutting lines 74 in addition to the outer holes 72 and the inner holes 73. The area of sections punched out when forming the conductor bars 63, 64 by forming the cutting lines 74 and the outer and inner holes 72, 73 it each plate 71 is less than the area of the punched out sections when forming the conductor bars 25 by forming the slits 32 in each plate 31 in the case of the first embodiment. That is, according to the second embodiment, the amount of waste produced by punching is relatively small.

(3) The pressing operation for forming the outer holes 72 and the inner holes 73 and the pressing operation for forming the cutting lines 74 are not performed simultaneously but are separately performed on each plate 71. Compared to the case where the outer holes 72, the inner holes 73, and the cutting lines 74 are formed in each plate 71 through a simultaneous pressing operation, the amount of cutting per pressing operation is less. This reduces the frictional force between the pressing die and the plate 71, so that the conductor bars 63, 64 are prevented from being deformed during the pressing operation.

The above-mentioned embodiments may be modified as follows.

In the second embodiment, the outer holes 72, the inner holes 73, and the cutting lines 74 may be simultaneously formed in each plate 71 through pressing.

In the second embodiment, both of the coupling portions 65 a, 65 b of the first conductor bar group 62 and the coupling portions 65 a, 65 b of the second conductor bar group 62 are bent such that their center portions project in the axial direction of the conductor bar assembly 61. However, either of the coupling portions 65 a, 65 b of the first conductor bar group 62 and the coupling portions 65 a, 65 b of the second conductor bar group 62 may be bent such that their center portions project in the axial direction of the conductor bar assembly 61.

In the second embodiment, each coupling portion 65 a, 65 b has a channel-like longitudinal cross-sectional shape. However, as long as each coupling portion 65 a, 65 b projects at its center portion in the axial direction of the conductor bar assembly 61, the coupling portion 65 a, 65 b may have an arcuate or triangular longitudinal cross-sectional shape.

In the first embodiment, the first angle θ1, which is a displacement angle between the inner terminal 27 and the outer terminal 26 of each first conductor bar 24, is greater than the second angle θ2, which is a displacement angle between the inner terminal 27 and the outer terminal 26 of each second conductor bar 25. Also, in the second embodiment, the first angle θ1, which is a displacement angle between the inner terminal 27 and the outer terminal 26 of each first conductor bar 63, is greater than the second angle θ2, which is a displacement angle between the inner terminal 27 and the outer terminal 26 of each second conductor bar 64. However, in each of the embodiments, the first angle θ1 may be smaller than the second angle θ2.

In the first embodiment, the coupling portions 28 a, 28 b are bent such that their center portion bulges along the direction of the thickness of each plate 31 at the same time as forming the eight slits 32 in the plate 31 through punching. However, the pressing operation for forming the slits in each plate 31 and the pressing operation for bending the coupling portions 28 a, 28 b may be performed separately.

In the first and second embodiments, integrated two plates are used as an insert in insert molding of the holding member 22. Then, the outer frames 33 and the inner frames 34 are removed. However, the holding member 22 may be insert molded after removing the outer frames and the inner frames 34.

In the first embodiment, the following configuration is applied to prevent the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portion 28 a, 28 b of the second conductor bar group 23 from contacting each other and being short-circuited. That is, each coupling portion 28 a, 28 b of the first conductor bar group 23 or each coupling portion 28 a, 28 b of the second conductor bar group 23 is bent such that its center portion bulges by a relatively great amount in the axial direction of the conductor bar group 23, and each coupling portions 28 a, 28 b of the other conductor bar group 23 is bent such that its center portion bulges by a relatively small amount in the axial direction of the conductor bar group 23. The direction in which the center portions of the coupling portions 28 a, 28 b with greatly bulging center portion bulge is a direction away from the conductor bar group 23 that is different from the conductor bar group 23 to which the coupling portions 28 a, 28 b of the greatly bulging center portions belong. The direction in which the center portions of the coupling portions 28 a, 28 b with slightly bulging center portion bulge is a direction toward the conductor bar group 23 that is different from the conductor bar group 23 to which the coupling portions 28 a, 28 b of the slightly bulging center portions belong. However, other configuration may be employed to prevent the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23 from contacting each other and being short-circuited.

For example, both of the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23 may be bent such that their longitudinal center portions bulge by a same amount in the axial direction of the corresponding conductor bar group 23. Also, the first conductor bar group 23 and the second conductor bar group 23 may be stacked on each other such that the direction in which the center portion of each coupling portion 28 a, 28 b of one of the conductive bar group 23 projects is a direction away from the other conductor bar group 23. Alternatively, the thickness of the coupling portions 28 a, 28 b of the first conductor bar group 23 and the second conductor bar group 23 may be less than the thicknesses of the outer terminals 26 and the inner terminals 27. Further, the first conductor bar group 23 and the second conductor bar group 23 may be stacked on each other such that the spaces between the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23 are maximized. Alternatively, an insulating sheet may be provided between the coupling portions 28 a, 28 b of the first conductor bar group 23 and the coupling portions 28 a, 28 b of the second conductor bar group 23. These modifications are advantages in that the shape of the first conductor bar group 23 and the shape of the second conductor bar group 23 can be made identical.

In the first embodiment, the first conductor bar group 23 and the second conductor bar group 23 do not need to have identical shapes when viewed along the center axis of the corresponding conductor bar group 23.

In the second embodiment, the first conductor bar group 62 and the second conductor bar group 62 do not need to have identical shapes when viewed along the center axis of the corresponding conductor bar group 62.

In the first and second, embodiments, the commutator 4 has fourteen segments, and each pair of the segments 14 that are spaced by 180 degrees are short-circuited by the short-circuit member 12. However, as long as the number of the segments 14 in the commutator 4 is represented by 2n (n is a positive even number), the number of the segments 14 does not need to be limited to that shown in the first and second embodiments. When the member of the segments 14 in the commutator 4 is expressed by 2n, the number of the conductor bars 24, 25 of the conductor bar groups 23 and the number of the conductor bars 63, 64 of the conductor bar groups 62 are each expressed by n.

For example, in the case where the commutator 4 has six segments 14, the short-circuit member 12 may have a conductor bar assembly 41 shown in FIG. 12 instead of the conductor bar assembly 21 shown in FIG. 3 or the conductor bar assembly 61 shown in FIG. 6. The conductor bar assembly 41 is formed by stacking a first conductor bar group 23 and a second conductor bar group 23, each having two first conductor bars 24 and two second conductor bars 25. The four conductor bars 24, 25 of each conductor bar group 23 are arranged at equal angular intervals to form a circle. The inner terminal 27 of each first conductor bar 24 is displaced from the outer terminal 26 of the same first conductor bar 24 along the circumferential direction of the conductor bar group 23 by a predetermined first angle θ1 (=90+(360/(4n))), specifically, by 112.5 degrees. The inner terminal 27 of each second conductor bar 25 is displaced from the outer terminal 26 of the same second conductor bar 25 along the circumferential direction of the conductor bar group 23 by a predetermined second angle θ2 (=90−(360/(4n))), specifically, by 67.5 degrees. The direction in which the inner terminal 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the first conductor bar group 23 is opposite to the direction in which the inner terminals 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the second conductor bar group 23. Each of the inner terminals 27 of the first conductor bar group 23 is aligned with the corresponding one of the inner terminals 27 of the second conductor bar group 23, and each of the outer terminals 26 of the first conductor bar group 23 is displaced from the corresponding one of the outer terminals 26 of second conductor bar group 23 with respect to the circumferential direction of the corresponding conductor bar group 23.

Alternatively, in the case where the commutator 4 has twelve segments 14, the short-circuit member 12 may have a conductor bar assembly 51 shown in FIG. 13 instead of the conductor bar assembly 21 shown in FIG. 3 or the conductor bar assembly 61 shown in FIG. 6. The conductor bar assembly 51 is formed by stacking a first conductor bar group 23 and a second conductor bar group 23, each having three first conductor bars 24 and three second conductor bars 25. The six conductor bars 24, 25 of each conductor bar group 23 are arranged at equal angular intervals to form a circle. The inner terminal 27 of each first conductor bar 24 is displaced from the outer terminal of the same first conductor bar 24 along the circumferential direction of the conductor bar group 23 by a predetermined first angle θ1 (=90+(360/(4n))), specifically, by 105 degrees. The inner terminal 27 of each second conductor bar 25 is displaced from the outer terminal 26 of the same second conductor bar 25 along the circumferential direction of the conductor bar group 23 by a predetermined second angle θ2 (=90−(360/(4n))), specifically, by 75 degrees. The direction in which the inner terminal 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the first conductor bar group 23 is opposite to the direction in which the inner terminals 27 is displaced from the outer terminal 26 in each conductor bar 24, 25 in the second conductor bar group 23. Each of the inner terminals 27 of the first conductor bar group 23 is aligned with the corresponding one of the inner terminals 27 of the second conductor bar group 23, and each of the outer terminals 26 of the first conductor bar croup 23 is displaced from the corresponding one of the outer terminals 26 of second conductor bar group 23 with respect to the circumferential direction of the corresponding conductor bar group 23.

In the first embodiment, the inner terminal 27 of each first conductor bar 24 is displaced from the outer terminal 26 of the same first conductor bar 24 along the circumferential direction of the conductor bar group 23 by the first angle θ1, specifically, by 101.25 degrees. The inner terminal 27 of each second conductor bar 25 is displaced from the outer terminal 26 of the same second conductor bar 25 along the circumferential direction of the conductor bar group 23 by the second angle θ2, specifically, by 78.75 degrees. Also, in the second embodiment, the inner terminal 27 of each first conductor bar 63 is displaced from the outer terminal 26 of the same first conductor bar 63 along the circumferential direction of the conductor bar group 62 by the first angle θ1, specifically, by 101.25 degrees. The inner terminal 27 of each second conductor bar 64 is displaced from the outer terminal 26 of the same second conductor bar 64 along the circumferential direction of the conductor bar group 23 by the second angle θ2, specifically, by 78.75 degrees. However, in either embodiment, the first angle θ1 and the second angle θ2 may be changed as necessary.

In the first embodiment, the number of the segments 14 in the commutator 4 is twice a positive even number, which is eight, but may be twice a positive odd number. In this case, the number of the conductor bars 24, 26 belonging to each conductor bar group 23 is half the number of the segments 14, that is, a positive odd number. Also, in this case, regarding some of the pairs of a conductor bar 24, 25 of the first conductor bar group 23 and a conductor bar 24, 25 of the second conductor bar group 23, of which the inner terminals 27 are aligned with each other, the displacement angle between the inner terminal 27 and the outer terminal 26 in one of the conductor bars 24, 25 is equal to that of the other of the conductor bars 24, 25.

In the second embodiment, the number of the segments 14 in the commutator 4 is twice a positive even number, which is eight, but may be twice a positive odd number. In this case, the number of the conductor bars 63, 64 belonging to each conductor bar group 62 is half the number of the segments 14, that is, a positive odd number. Also, in this case, regarding at least some of the pairs of a conductor bar 63, 64 of the first conductor bar group 62 and a conductor bar 63, 64 of the second conductor bar group 62, of which the inner terminals 27 are aligned with each other, the displacement angle between the inner terminal 27 and the outer terminal 26 in one of the conductor bars 63, 64 is equal to that of the other of the conductor bars 63, 64.

The shape of the insulation member 13 and the shape of the holding member 22 are not limited to those described in the first and second embodiments. For example, the joining portion 13 a of the insulation member 13 and the boss 22 a of the holding member 22 may be omitted, and the short-circuit member 12 may be arranged at one end of the insulation member 13. Alternatively, the holding member 22 may be omitted, so that the short-circuit member 12 includes only the conductor bar assembly 21 or 61. 

1. A short-circuit member comprising a first conductor member group and a second conductor member group, each conductor member group including a plurality of conductor members that are arranged to form a circle, the number of the conductor members belonging to the first conductor member group and the number of the conductor members belonging to the second conductor member group being equal to each other and represented by n; wherein each conductor member has an outer terminal located at an outer portion with respect to a radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling portion coupling the outer terminal and the inner terminal to each other, wherein the inner terminal of each conductor member is displaced from the outer terminal of the same conductor member with respect to a circumferential direction of the corresponding conductor member group; wherein the first conductor member group and the second conductor member group are stacked on each other such that the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the first conductor member group is opposite to the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the second conductor member, and wherein each inner terminal of the first conductor member group is aligned with a corresponding one of the inner terminals of the second conductor member group, and wherein each outer terminal of the first conductor member group is displaced from any one of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group.
 2. The short-circuit member according to claim 1, wherein, regarding each pair of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, the linear distance between the inner terminal and the outer terminal of one of the conductor members of the first conductor member group is different from the linear distance between the inner terminal and the outer terminal of the other conductor member of the second conductor member group.
 3. The short-circuit member according to claim 1, wherein, regarding at least some of the pairs of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, a first angle, which is a displacement angle between the inner terminal and the outer terminal in one of the conductor members of the first conductor member group, is different from a second angle, which is a displacement angle between the inner terminal and the outer terminal of the other conductor member of the second conductor member group.
 4. The short-circuit member according to claim 3, wherein the number of the conductor member belonging to the first conductor member group and the number of the conductor member belonging to the second conductor member group are even numbers, and wherein, regarding all the pairs of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, the first angle is different from the second angle.
 5. The short-circuit member according to claim 4, wherein the first angle is represented by (90+(360/(4n))°, and the second angle is represented by (90−(360/4n))°, the conductor members belonging to each conductor member group include first conductor members and second conductor members, wherein the first conductor members are consecutively arranged along the circumferential direction of the conductor member group and make up half of the conductor member group, the number of the first conductor members being represented by n/2, wherein the second conductor members are consecutively arranged along the circumferential direction of the conductor member group and make up the other half of the conductor member group, the number of the second conductor members being represented by n/2, and wherein the inner terminals of the conductor members belonging to each conductor member group are arranged at equal angular intervals along the circumferential direction of the conductor member group.
 6. The short-circuit member according to claim 5, wherein the first conductor member group and the second conductor member group have a same shape, wherein each inner terminals of each conductor member group is arranged to be axisymmetric with a corresponding one of the inner terminals with respect to a first straight line that passes through the center of the conductor member group, wherein each outer terminals of each conductor member group is arranged to be axisymmetric with a corresponding one of the outer terminals with respect to a second straight line that passes through the center of the conductor member group and is perpendicular to the first straight line, and wherein the first conductor member group and the second conductor member group are stacked on each other in a state where one of the first conductor member group and the second conductor member group are inverted about the first straight line.
 7. The short-circuit member according to claim 1, wherein either the coupling portion of each of the conductor members belonging to the first conductor member group and the coupling portion of each of the conductor members belonging to the second conductor member group is bent such that its center portion bulges in an axial direction of the corresponding conductor member group, and wherein the direction in which the center portions bulge from the corresponding conductor member group is a direction away from the other conductor member group.
 8. The short-circuit member according to claim 7, wherein each pair of the coupling portions with bulging center portions that are adjacent to each other in the circumferential direction of the corresponding conductor member group contact each other before the coupling portions are bent, and separate from each other only after the coupling portions are bent.
 9. A commutator comprising: segments the number of which is represented by 2n, n being a positive integer; and short-circuit member having a first conductor member group and a second conductor member group, each conductor member group including a plurality of conductor members that are arranged to form a circle, the number of the conductor members belonging to the first conductor member group and the number of the conductor members belonging to the second conductor member group being equal to each other and represented by n; wherein each conductor member has an outer terminal located at an outer portion with respect to a radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling portion coupling the outer terminal and the inner terminal to each other, wherein the inner terminal of each conductor member is displaced from the outer terminal of the same conductor member with respect to a circumferential direction of the corresponding conductor member group, wherein the outer terminal of each conductor member is connected to the corresponding one of the segments; wherein the first conductor member group and the second conductor member group are stacked on each other such that the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the first conductor member group is opposite to the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the second conductor member; wherein each inner terminal of the first conductor member group is aligned with a corresponding one of the inner terminals of the second conductor member group, and wherein each outer terminal of the first conductor member group is displaced from any of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group.
 10. The commutator according to claim 9, wherein, regarding each pair of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, the linear distance between the inner terminal and the outer terminal of one of the conductor members of the first conductor member group is different from the linear distance between the inner terminal and the outer terminal of the other conductor member of the second conductor member group.
 11. The commutator according to claim 9, wherein, regarding at least some of the pairs of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, a first angle, which is a displacement angle between the inner terminal and the outer terminal in one of the conductor members of the first conductor member group, is different from a second angle, which is a displacement angle between the inner terminal and the outer terminal of the other conductor member of the second conductor member group.
 12. The commutator according to claim 11, wherein the number of the conductor member belonging to the first conductor member group and the number of the conductor member belonging to the second conductor member group are even numbers, and wherein, regarding all the pairs of a conductor member of the first conductor member group and a conductor member of the second conductor member group, of which the inner terminals are aligned with each other, the first angle is different from the second angle.
 13. The commutator according to claim 12, wherein the first angle is represented by (90+(360/(4n))°, and the second angle is represented by (90−(360/4n))°, the conductor members belonging to each conductor member group include first conductor members and second conductor members, wherein the first conductor members are consecutively arranged along the circumferential direction of the conductor member group and make up half of the conductor member group, the number of the first conductor members being represented by n/2, wherein the second conductor members are consecutively arranged along the circumferential direction of the conductor member group and make up the other half of the conductor member group, the number of the second conductor members being represented by n/2, and wherein the inner terminals of the conductor members belonging to each conductor member group are arranged at equal angular intervals along the circumferential direction of the conductor member group.
 14. The commutator according to claim 13, wherein the first conductor member group and the second conductor member group have a same shape, wherein each inner terminals of each conductor member group is arranged to be axisymmetric with a corresponding one of the inner terminals with respect to a first straight line that passes through the center of the conductor member group, wherein each outer terminals of each conductor member group is arranged to be axisymmetric with a corresponding one of the outer terminals with respect to a second straight line that passes through the center of the conductor member group and is perpendicular to the first straight line, and wherein the first conductor member group and the second conductor member group are stacked on each other in a state where one of the first conductor member group and the second conductor member group are inverted about the first straight line.
 15. The commutator according to claim 9, wherein either the coupling portion of each of the conductor members belonging to the first conductor member group and the coupling portion of each of the conductor members belonging to the second conductor member group is bent such that its center portion bulges in an axial direction of the corresponding conductor member group, and wherein the direction in which the center portions bulge from the corresponding conductor member group is a direction away from the other conductor member group.
 16. The commutator according to claim 15, wherein each pair of the coupling portions with bulging center portions that are adjacent to each other in the circumferential direction of the corresponding conductor member group contact each other before the coupling portions are bent, and separate from each other only after the coupling portions are bent.
 17. An armature comprising: a rotary shaft; an armature core fixed about the rotary shaft, a coil being wound about the armature core; and a commutator that is fixed about the rotary shaft, segments of the commutator are electrically connected to the coil, wherein the commutator includes: said segments the number of which is represented by 2n, n being a positive integer, and short-circuit member having a first conductor member group and a second conductor member group, each conductor member group including a plurality of conductor members that are arranged to form a circle, the number of the conductor members belonging to the first conductor member group and the number of the conductor members belonging to the second conductor member group being equal to each other and represented by n, wherein each conductor member has an outer terminal located at an outer portion with respect to a radial direction of the corresponding conductor member group, an inner terminal located at an inner portion with respect to the radial direction of the corresponding conductor member group, and a coupling portion coupling the outer terminal and the inner terminal to each other, wherein the inner terminal of each conductor member is displaced from the outer terminal of the same conductor member with respect to a circumferential direction of the corresponding conductor member group, wherein the outer terminal of each conductor member is connected to the corresponding one of the segments, wherein the first conductor member group and the second conductor member group are stacked on each other such that the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the first conductor member group is opposite to the direction in which the inner terminal is displaced from the outer terminal in each conductor member of the second conductor member, and wherein each inner terminal of the first conductor member group is aligned with a corresponding one of the inner terminals of the second conductor member group, and wherein each outer terminal of the first conductor member group is displaced from any of the outer terminals of the second conductor member with respect to the circumferential direction of the first conductor member group. 